1. Field of the Invention
The present invention generally relates to printer cartridges that are used within image forming devices, and more particularly to a cam device that separate rollers within the printer cartridge in non-operating conditions.
2. Description of the Related Art
Mono and color laser printers use a charge roller with an electrically conductive coating to create a uniform charge on the photoconductive drum. A laser is then used to discharge portions of this photoconductive drum surface in order to form a latent image thereon. The charge on the surface of the photoconductive drum that is exposed by the laser is reduced, allowing toner to adhere. This toner is then transferred to a print medium and subsequently gets melted thereon by a fuser to create a printed image.
A charge roller needs to be pressed against the photoconductive drum in order to create an initial uniform charge on the photoconductive drum. However, if the charge roller and the photoconductive drum are allowed to remain in contact for extended periods of time chemicals in the charge roller can migrate on the surface of the photoconductive drum causing print defects. This may occur when aftermarket units are stored for months before shipment to customers. Extended storage may also create a compression line on the charge roller which can lead to defects. Thus, it is desired that the charge roller is separated from the photoconductive drum until they are ready to be used.
Some manufacturers solve this problem by installing a separator sheet between the charge roller and the photoconductive drum. Others use a throw away wedge that lifts the charge roller off the photoconductive drum. In both these cases, the customer must remove these items before using the printer. Failing to remove these items or touching nearby parts in the printer may lead to machine malfunction and customer dissatisfaction.
In addition to separator sheets or wedges, some manufacturers have used cam devices. These cam devices are designed to provide interference fit between the cam and charge roller shaft to prevent the cam from engaging during vibration or drop conditions. However, such interference fit can cause noise or squealing during normal printing operations and this further reduces the reliability of the cam. Further, any radial interference between the cam and the charge roller shaft can create a frictional drag such that the charge roller stalls or slips against the photoconductive drum which can cause print defects.
Thus, there is a need to provide a mechanism that addresses at least some of the above problems yet provide a reliable separation between the charge roller shaft and the photoconductive drum.